Hi @DervanilJunior-4636 · Welcome to Q&A platform and thanks for your query.
The problem with empty string collection is, we cannot infer an empty list to be of type string collection. It could be of some other type as well. There is a bug already open with product team for this issue. However, there is no ETA for a fix as of now.
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@Dervanil Junior · You can try checking if the claim is present first https://learn.microsoft.com/en-us/azure/active-directory-b2c/general-transformations#doesclaimexist
Or initialize it with a default value.